Removal of disease such as atherosclerotic plaque, thrombus and other types of obstructions and partial obstructions from internal body lumens or cavities using advanceable, rotating operating heads is a well-established interventional technique. Numerous interventional catheters have been conceived and developed. Most of these systems require placement of a guiding catheter and guide wire prior to introduction of the interventional catheter and placement of the interventional catheter at the target operating site. Many of these prior art systems incorporate mechanical aspiration systems to remove the ablated material from the site and some systems incorporate, or are used in conjunction with, other mechanisms such as distal filters for preventing removed material from circulating in the blood stream.
In interventional catheters that employ a “cutting head,” cutter structures must be benign during navigation of the operating head to and from the interventional target site, yet effectively remove material during the operation. In addition, cutter structures must effectively remove diseased, or undesired, material without damaging delicate neighboring tissue, such as blood vessel walls or other healthy tissue, which often surrounds and may be attached to the undesired material. Thus, it is important for cutter structures of interventional catheters to accurately and reliably differentiate between the diseased material and healthy tissue.
Differential cutting blades exert high shear forces against relatively hard substrates to cut or ablate relatively hard, inelastic, material. Softer, elastic structures, such as healthy tissue, blood vessel walls and the like, are deformed rather than cut by differential cutting blades, thereby reducing the shear forces and protecting elastic structures from damage. Less elastic material does not deform when contacted by a differential cutting blade, and shear stresses are consequently exerted on less elastic material to cut or scrape and ablate the material without damaging elastic tissue in proximity. In this manner, fragments of diseased, undesirable material are removed by differential cutting blades, while the more elastic, healthy tissue remains undamaged.
U.S. Pat. No. 4,445,509 describes differential cutting in the context of an atherectomy device. This patent describes a cutter assembly having a plurality of cutting flutes, each cutting flute having a blade surface operating according to the principle of differential cutting. Aspiration ports are provided in the body of the cutter assembly for collection and removal of particulates and liquids from the site of the intervention. U.S. Pat. Nos. 6,565,588 and 6,818,001, together with U.S. Patent Publication 2004/0006358 A1, also disclose the use of cutter assemblies to separate undesired material from underlying tissue at a site of intervention, with an aspiration system incorporating aspiration ports provided between the cutting surfaces for withdrawal of liquids and particulate debris from the site.
Some interventional catheters use diamond grit on a cutting surface in an effort to provide highly divided, small particle size debris. Relatively coarse diamond grit is more likely to damage elastic, healthy tissue such as blood vessel walls. Relatively fine diamond grit has slow material removal rates, requiring the use of higher rotational speeds. The use of grit or abrasive particles or surfaces can, however, be beneficial and generate small particulate debris, providing effective material removal.
Alternative material removal systems may incorporate an Archimedes screw-type mechanism at a distal end of an interventional catheter, in which material is caught between the threads of the screw and withdrawn from the site using mechanical rotational motion. Material removal systems may also incorporate a plaque excision device having a blade that traverses and exits a window at a distal end of an interventional catheter to scrape plaque from a vessel wall and collect it in an internal collection space provided in the distal end of the interventional catheter.
In any of these material removal systems, removal of debris generated at the site of intervention is critical to prevent distal embolization of the debris. Several prior art interventional catheters provide for aspiration of liquids and/or debris from the material removal site. Aspirating thrombectomy catheters employ a catheter having a vacuum system to draw thrombus into the catheter and remove it from the site. Many interventional catheters incorporate, or are used with, a distal filter mechanism that traps debris before it can be carried away in the bloodstream. Numerous interventional catheters also provide infusion of a liquid to the site of the intervention. Infused liquids may assist in the material removal process, or may be provided as diagnostic or therapeutic materials prior to, during or following an intervention.
Despite the many and varied approaches to material removal from lumens such as blood vessels and the availability of many and varied material removal systems, challenges remain in providing systems for removing material from a lumen, such as a blood vessel, safely, reliably and effectively, without causing complications. The safety and reliability of the system is manifestly critical. Recovery of debris generated during a material removal operation, or breaking down the debris to a particle size that will not produce blood vessel damage or embolic events, is essential.